This study is a randomized clinical trial (RCT) evaluating the effect of N-acetylcystein on biomarkers of platelet activation and coronary reperfusion in patients undergoing percutaneous coronary intervention. Double blind randomized clinical trial on 100 patients in 2 groups (intervention & control) is conducted. Patients with confirmed ST-elevation myocardial infarction included in this study. Patients were excluded if they had: emergency for cardiac bypass; cardiogenic shock and rescue percutaneous coronary intervention. Patients in Intervention group were administered 100 mg/kg Iv bolus N-acetylcystein and then 480mg intracoronary and 10mg/kg/h over 12 hours after percutaneous coronary intervention and patients in control group received standard regimens. Primary outcome was platelet activation biomarkers assessment before and 24 hours after percutaneous coronary intervention and secondary outcome was effect of N-acetylcystein on CK-MB and high sensitive Troponin T, 6 and 12 hours after percutaneous coronary intervention.Patients were assessed for coronary blood flow after percutaneous coronary intervention with the use of TIMI flow and myocardial blush grade.